1. Technical Field
The present invention generally relates to lighting systems, and more particularly, to fluorescent lamps.
2. Background
Many industries and applications need backlighting for an information source. In particular, transmissive liquid crystal displays (LCDs) have become very popular in many electronic media. LCDs are useful in applications such as avionics, laptop computers, video cameras, and automatic teller machines. However, many LCDs require backlighting to illuminate the information being displayed.
Various systems perform the backlighting function in conventional displays. For example, one way to backlight an information source employs an array of conventional straight tubular fluorescent lamps. Low costs associated with such conventional lamps control costs, but they are sometimes inadequate for particular applications. For instance, in avionics applications, the poor color quality of the phosphors and the short lamp life of conventional lamps, among other shortcomings, limit their usefulness.
To avoid the various problems with conventional lamps, many manufacturers employ customized lamps, such as tubular serpentine lamps. Unlike conventional fluorescent lamp arrays, custom-made serpentine lamps commonly provide good color characteristics, high luminance uniformity, and long lamp life. These lamps are typically hand made, and consequently, are comparatively costly. Moreover, these lamps are extremely fragile and difficult to install. Additionally, to optimize the light output, conventional serpentine backlight systems include a diffuser and reflective cavity, adding further cost to the overall information source. Therefore, while custom-made tubular serpentine lamps may meet certain standards for the backlighting function, the high cost and fragility detract from the advantages they offer.
A third alternative for backlighting information sources is flat fluorescent lamps. An exemplary flat fluorescent lamp described in U.S. Pat. No. 5,343,116, issued Aug. 30, 1994, to Winsor, comprises a substrate fritted to a transparent cover lid, forming an enclosure. Diffuse channels are formed into the substrate in the interior of the enclosure. Standard phosphors are added to the interior of the enclosure which is further flushed with a material for emitting energy, such as argon or mercury. Energy is emitted in the form of visible light when an electric potential is introduced to the lamp by two electrodes, with one electrode placed at each end of the diffuse channel. Plasma or other emissive material is ignited through sparking caused by the electric potential between the two electrodes. Such lamps offer ruggedness and lower manufacturing costs than serpentine tubular lamp alternatives.
However, the serpentine channel in these flat lamps is difficult to use in its optimal configuration. To achieve the desired light output without putting undue thermal stress on the lamp, the channel needs to be reduced in width and depth. As the surface area of the lamp must remain constant, the length of the channel needs to be increased to compensate for the reduction in width and depth.
This increased channel length requires a significantly higher voltage to achieve lamp ignition. When the electrodes spark the emissive material, it creates an arc that travels in one direction and has one ignition segment. The longer the diffuse channel, the longer the arc has to travel, and consequently, the greater the voltage that is needed to start the lamp. Due to the large voltage required to start conventional serpentine flat fluorescent lamps, the electronics that are required to perform that function can be costly, especially in applications having little space to spare for physically large power sources.